Polyimides derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 2,2-bis[4-(aminophenoxy)phenyl]hexafluoropropane are useful, inter alia, for the production of electronic coatings on semiconductor wafers, such as polysilicon wafers. In order to apply solutions or such polyimides to the wafers spin coating procedures are used, and in these operations purity, integrity, and uniformity of the resultant polyimide coating are essential.
Unfortunately it has been discovered that in humid atmospheres (e.g., 40% relative humidity or above) solutions of such polyimides in some commonly used solvents (e.g., N-methylpyrrolidone) tend to be unstable in the sense that during spin coating operations undesirable precipitate formation occurs on the rotating surface of the wafer. The result is that the coating loses adhesion to the wafer and flies off of it during spin coating.
The need thus exists for solutions of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride/2,2-bis[4-(aminophenoxy)phenyl]hexafluoropropane polyimides which do not undergo undesirable precipitate formation on rotating wafer surfaces when used in spin coating operations even if conducted under conditions of 55% relative humidity. This invention is deemed to fulfill this need in an effective and efficient manner.